I. Technical Field
The present invention relates to a small speaker, particularly an ultra-small speaker called a receiver, and to a device including the small speaker.
II. Description of the Related Art
Along with the popularization of portable music players, recent years have seen heavy use of earphones and headphones for easy music reproduction and enjoyment indoors and outdoors. Furthermore, with the advancement of an aging society, the demand for hearing aids has increased and increased use of receivers, which are ultra-small speakers used in sound reproduction in hearing aids, is expected.
Among earphones intended primarily for such music reproduction or hearing aid receivers, inner ear earphones or receivers which are inserted into the external auditory canal of the ears are widely used. Taking into consideration the wearing comfort of a user, it is preferable that the configuration of such an inner ear earphone or receiver be compact. In particularly, for hearing aids that a user wears in the ears for prolonged periods over the course of everyday life, there is a strong demand for small receivers that are hardly felt by the user when worn.
Furthermore, there is a demand for prolonged battery life, particularly in hearing aids, to enable use over extended periods of time. As such, in hearing aids, it is important to suppress the power consumed by the receiver. In order to suppress power consumption, it is preferable that the acoustic efficiency of the receiver be increased to allow sufficient sound volume to be obtained even with low power. However, speaker miniaturization and improvement of acoustic efficiency often contradict each other, and thus, generally, the size of a speaker becomes big when attempting to increase the acoustic efficiency of the speaker.
As one conventional technique for solving this problem, there is a speaker described in Unexamined Japanese Patent Application Publication Number 2-44899. FIG. 13 is a structural cross-sectional view of a conventional speaker described in Unexamined Japanese Patent Application Publication Number 2-44899. As shown in FIG. 13, the conventional speaker includes a first speaker unit 1, a second speaker unit 2, a first chassis 3 which holds the first speaker unit, a second chassis 4 which holds the second speaker unit 2 and the first chassis 3. Inside the speaker, an air passage 5 is formed by the outer periphery of the first chassis 3 and the inner periphery of the second chassis 4.
The first speaker unit includes a diaphragm 6, a suspension 7 which supports the entirety of the outer periphery of the diaphragm 6, a voice coil 8 which is fixed to the diaphragm 6, and a magnetic circuit unit. The magnetic circuit unit includes a yoke 9, a magnet 10, and a plate 11. Furthermore, in the magnetic circuit unit, a magnetic air gap 12 is formed by the inner periphery of the yoke 9 and the outer periphery of the plate 11. The voice coil 8 is held inside the magnetic air gap 12.
The second speaker unit 2 has the same structure as the first speaker unit 1, and thus detailed description shall not be repeated.
The operation of the conventional speaker configured in the manner described above shall be described. The sound generated from a diaphragm 13 of the second speaker unit 2 is radiated to the outside of the speaker via the air passage 5 formed by the outer periphery of the first chassis 3 and the inner periphery of the second chassis 4. On the other hand, the sound generated from the diaphragm 6 of the first speaker unit 1 is directly radiated to the outside of the speaker. As a result, a combined sound of the sound from the first speaker unit 1 and the sound from the second speaker unit 2 which is radiated through the air passage 5 is reproduced.
In this manner, the conventional speaker shown in FIG. 13 achieves miniaturization by arranging two speaker units in series. Specifically, arranging two speaker units on top of each other in the vibration direction of the diaphragms allows for miniaturization of the speaker as a whole compared to when two speakers are arranged in the same plane. Furthermore, since the sounds outputted from the two speakers are combined into one, it is possible to improve acoustic efficiency.